1. Field of the Invention
The present invention relates to a direct-current power supply system (hereinafter, the system is called a "DC power supply system") for converting an alternating current (AC) supplied from an alternating-current power supply (hereinafter, the system is called an "AC power supply") into a direct current (DC). More particularly, the DC power supply system relates to a system having a reactor inserted into an AC input side of the DC power supply system.
2. Description of Prior Art
In a conventional capacitor-input type DC power supply system, since an input current only flows while an input voltage is larger than a capacitor voltage, that is, "the input voltage&gt;the capacitor voltage" and, there are no elements which limit the input current, the input current gets to be a pulse current having a spike value which is high and having an electrified width which is narrow. To prevent the input current from getting to be the pulse current, a method for inserting a reactor into an input circuit of the capacitor-input type DC power supply system so as to improve a power factor caused between the input current and the input voltage and to restrict a higher harmonic ingredient is previously proposed. However, for getting these effects such that the power factor is improved and the higher harmonic ingredient is restricted, it needs to insert the reactor which has a high inductance. Moreover, when the inductance of the reactor increases, if anything, a degree of a fall of the input voltage is large and a maximum output power of the system falls.
Thus, applicants, for improving a waveform of the input current and the input direct current voltage by using a reactor having a lower inductance, have proposed a DC power supply system for forcibly energizing the reactor so as to improve the power factor and the decrease of the higher harmonic ingredient. Furthermore, applicants also have proposed a method of restricting a vibration noise of the reactor caused by energizing the reactor.
FIG. 6 is an electronic circuit diagram showing an example of this type of a DC power supply system. In this DC power supply system 100, a reactor 102 is inserted in series into one output end of an AC power supply 101, such as a commercial power supply, and so on.
The other end of the reactor 102 is connected to one input end of a first diode bridge 103 consisting of a short circuit and to one input end of a second diode bridge 104 consisting of rectifier circuit.
The first diode bridge 103 is constituted by four diodes (fifth diode D5, sixth diode D6, seventh diode D7 and eighth diode D8). The second diode bridge 104 is constituted by four diodes (first diode D1, second diode D2, third diode D3 and fourth diode D4).
Respective other input ends of the first diode bridge 103 and the second diode bridge 104 are connected to the other output end of the AC power supply 101.
Both output ends of the first diode bridge 103 are connected to a switching element 105, such as a bipolar transistor, MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and so on. In FIG. 6, as the switching element 105, the bipolar transistor is used.
The switching element 105 is connected to control means 106 consisting of a microprocessor or other similar processing unit so as to be gated on and off by the control means 106.
Incidentally, in FIG. 6, referential numeral 107 shows voltage doubler capacitor, referential numeral 108 shows a smoothing capacitor and referential numeral 109 shows a load.
In addition, FIG. 7 is an electronic circuit diagram showing another example of this type of a DC power supply system which has an Insulated Gate Bipolar Transistor (IGBT) 105a as the switching element.
The first diode bridge circuit 103 consisting of the short circuit is adapted to make the IGBT 105a consisting of the switching element 105 control so that the switching element 105 is gated on and off by a gate driver power supply unit 106a consisting of the control means 106 and a drive unit (drive power supply unit).
Remaining elements of the DC power supply system 100a except for the switching element are the same as corresponding elements of the DC power supply system 100. Incidentally, in FIG. 7, the voltage doubler capacitors 107 and the load 109 are omitted.
A predetermined power-factor improvement pulse is supplied from the control means 106 to the switching element 105 for a predetermined period of time since an alternating current voltage of the AC power supply 101 has just passed through each zero points (zero-crossing points) so that the switching element 105 is controlled so as to be gated on and off. According to the ON-OFF control of the switching element 105, both output ends of the AC power supply 101 are short-circuited for a short period of time through the reactor 102 and the first diode bridge 103 so as to forcibly energize the reactor 102. The energy of the reactor 102 causes an enlargement of a conducting period of time (that is, a conducting angle) of the input current of the system. As a result of that, it is possible to improve the power factor of the system and to reduce the higher harmonic ingredient without increasing the inductance of the reactor 102.
Furthermore, in the case where a vibration noise is caused by rapid current change in accordance with forcibly energizing the reactor 102 and cutting off it, by supplying a predetermined noise reduction pulse to the switching element 105 after a predetermined delay period of time since the power-factor improvement pulse is supplied thereto, the short circuit of the reactor 102 is opened so that the vibration noise of the reactor 102 is also decreased.
The AC supplied from the AC power supply system 101 flows through the first diode bridge circuit 103 which is short-circuited by the power-factor improvement pulse for a short period of time and, when the first diode bridge circuit 103 is opened, the AC is switched and flows to the side of the second diode bridge circuit 104. When the first diode bridge 103 is short-circuited by the noise reduction pulse, a discontinuous current including a reverse recovery current of the second diode bridge circuit 104 flows between the first diode bridge circuit 103 and the second diode bridge circuit 104.
FIG. 8 is a wave form chart showing a current value (ampere(A)) of the discontinuous current including the reverse recovery current according to a time (millisecond(MS)) in first short circuit time (T1) at which the first diode bridge circuit 103 is short-circuited and in re-short circuit time at which the first diode bridge circuit 103 is short-circuited again. That is, FIG. 8A is a wave form chart showing a current value (A) of the discontinuous current flowing through the side of the second diode bridge circuit 104 and FIG. 8B is a wave form chart showing a current value (A) of the discontinuous current flowing through the side of the first diode bridge circuit 103.
In addition, FIG. 9(A) is an enlarged wave form chart showing a current value (A) of the discontinuous current in FIG. 8(A) flowing close to the first diode bride 103 and FIG. 9(B) is an enlarged wave form chart showing a current value (A) of the discontinuous current in FIG. 8(B) flowing close to the first diode bride 103.
In the above DC power supply system, the first diode bridge 103, the second diode bridge 104 and the switching element 105 are constructed by different individual semiconductor modules M3, M4 and M5, respectively. Therefore, there are many output terminals of the first diode bridge 103, the second diode bridge 104 and the switching element 105 (the semiconductor modules M3, M4 and M5).
That is, the number of the output terminals of the first diode bridge 103 are four terminals, as shown by small circles of a1.about.a4 in FIG. 6, the number of the output terminals of the second diode bridge 104 are four terminals, as shown by small circles of b1.about.b4 therein and the number of the output terminals of the switching element 105 are three terminals, as shown by small circles of c1.about.c3 therein. So, the sum of the terminals of the first diode bridge 103, the second diode bridge 104 and the switching element 105 is eleven terminals. For this reason, an efficiency of an assembly operation including connection operations of each of the first diode bridge 103, the second diode bridge 104 and the switching element 105 is lowered, and the reliability thereof is reduced.
Moreover, in the first diode bridge 103, the second diode bridge 104 and the switching element 105, radiating means for radiating heat therein are individually and respectively provided. These respective radiating means are constructed so as to correspond to these respective electrical rated value of the first diode bridge 103, the second diode bridge 104 and the switching element 105, respectively. That is, since in the above DC power supply system it must be provided with the plurality of radiating means, it is disturbed to make the DC power supply system small-sized and light.
Furthermore, a path, through which the discontinuous current caused by the switching operation of the switching element 105 and the reverse recovery current shaped as a spike and caused by the short circuit of the noise reduction pulse flow, is shown in FIG. 6 such that the discontinuous current and the reverse current flow through a first diode D1 of the second diode bridge circuit 104, a fifth diode D5 of the first diode bridge circuit 103, the switching element 105 and a eighth diode D8 (a first diode D1 of the second diode bridge circuit 104.fwdarw.a fifth diode D5 of the first diode bridge circuit 103.fwdarw.the switching element 105.fwdarw.an eighth diode D8). Since the discontinuous current and the reverse current flow between the semiconductor module M3, M4 and M5, electromagnetic wave noise radiated to an outside portion of these respective modules M3, M4 and M5 is increased.